Distributed Energy Resources: Issues and Challenges

Abstract

Distributed energy resources DER constitute a relatively new paradigm in the electric power industry. The concept is gaining popularity because of the inherent modularity of DERs. They can be regarded as more flexible power sources, albeit with limited capacity, than centralized power units. DERs are power generation or storage units that are connected directly to the distribution network or connected to the network on the customer side of the meter. These energy sources can include microturbines, fuel cells, wind power, solar power, and several forms of energy storage. If barriers can be removed, DERs can be valuable resources to the power generation and distribution industry. They have the potential to improve reliability, power quality, and environmental pollution while deferring transmission and distribution T&D capital expenditures. However, careful studies are required to prove their true potential. In this special issue devoted to "Distributed Energy Resources-Potentials for the Electric Power Industry," eight high-quality papers out of the nineteen papers received were selected for publication. Each paper was reviewed externally by at least two leading researchers in the field. The topics addressed by the papers include a wide array of issues faced by the power industry as it readies itself for a possible influx of distributed resources in the near future. These are as follows: • DER modeling; • Storage aspects of DER; • Microgrids; • Economic and operational aspects of DER; • Impact on power quality and reliability; and • Interconnection standards. Although different circles define distributed generation DG in somewhat different perspectives, the most widely accepted version defines it as being a generation source located in proximity to load centers and having a generating capacity of anywhere from 10 kW to 50 megawatts. Often, such generating sources use non-conventional fuels, and many of the units are designed to produce both electricity and heat, in applications simply known as combined heat and power CHP. This represents a departure from the current industry practice of locating very large fossil-fired generating sources at remote locations, closer to the fuel source and transmitting the generated power over high-voltage transmission lines to load centers. Many of the DER technologies, such as those that depend on solar power, wind power, and biomass, are inherently renewable in nature. Since solar and wind power outputs depend on an intermittent resource, predicting the amount of power that will be available at certain times of the day often becomes difficult. With large amounts of intermittent generation, operating the renewable DER within an existing electric utility's system can bring about some uncertainties in both the generating source behavior and the network behavior. Studies have shown that at certain penetration levels, one may start to see problems with interconnection. Some suggest this level to be 15%, whereas some suggest 30%. However , whatever the penetration level is, it is clear that the resource variability will most likely have an impact on system operations, including voltage and frequency and, in general, power quality. Therefore, many advocate using distributed energy storage in the system to overcome the variability in the power output from the renewable DERs. Storage also helps provide the needed regulation capacity when load demands change from minute to minute.